2021-12-22_PERMIT FILE - C1981019 (2)

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6 6.0 DETERMINATION OF MATERIAL DAMAGE 6.1 Regulatory Basis The 1988 Mined Land Reclamation Division report “A Description of the Material Damage Assessment Process Pertaining to Alluvial Valley Floors, Surface Water, Ground Water and Subsidence at Coal Mines” (MLRB 1988) describes the regulatory basis for material damage assessments: The Colorado Surface Coal Mining Reclamation Act contains the following prohibition with respect to alluvial valley floors: No permit or permit revision shall be approved unless it is demonstrated that the surface coal mining operations would not materially damage the quantity or quality of surface water or ground water systems that supply an alluvial valley floor (34-33-114(2)(e)). The "Regulations of the Mined Land Reclamation Board For Coal Mining" define material damage with respect to alluvial valley floors as: Changes in the quality or quantity of the water supply to any portion of an alluvial valley floor where such changes are caused by surface coal mining and reclamation operations and result in changes that significantly and adversely affect the composition, diversity or productivity of vegetation dependent on subirrigation, or which result in changes that would limit the adequacy of the water for flood irrigation of the irrigable land acreage existing prior to mining. (Rule 1.04(72)). 6.2 Irrigation Water Salinity Numerous studies have been conducted which relate plant growth and physiological functions to soil salinity. Most of the studies indicate that in the absence of soil moisture deficiency, crop yield is directly related to the average soil salinity in the portion of the root zone where maximum water uptake occurs during the growing season. These thresholds are based on agricultural species relative salt tolerance based on salinity level at initial yield decline and yield decrease per unit increase in salinity beyond the threshold level. The relationship between irrigation water salinity and soil solution salinity is greatly affected by irrigation frequency and by the percent of applied water which percolates below the rooting zone. The Mined Land Reclamation Board report (1988) uses an adjustment factor of 1.5 to account for applied irrigation water due to the concentrating effect of evapotranspiration when calculating field irrigation water conductance thresholds. Table 4 presents the field salinity thresholds, which were calculated based on field observations of composition and Colorado State University Extension fact sheets 0.503 - Managing Saline Soils and 7.227 - Growing Turf on Salt-Affected Sites (described in Section 2.0), along with the field irrigation water conductance thresholds. Irrigation water quality (conductance) was provided by Colowyo, collected from the LGSC surface water monitoring location, which is located below Colowyo’s lowest discharge point (Streeter Pond) on Goodspring Creek, but